The shiitake mushroom is native to Japan, China, and other East Asian countries, where it naturally grows on fallen trees in the forest: hence the common name, “black forest mushroom.” Deliberate cultivation of shiitake, both for food and medicine, is of ancient origin.

During the Ming Dynasty period (1368-1644), shiitake developed a reputation as a “tonic,” a substance said to increase energy, prevent disease, aid convalescence from illness, and slow bodily deterioration caused by aging. It was also used more specifically to treat respiratory illnesses, liver diseases, and intestinal infestation with worms.

As yet, there are no proposed uses of shiitake mushroom or shiitake mushroom extracts that are supported by reliable scientific evidence.

Current investigation of shiitake focuses primarily on the potential immune-stimulating and anti-cancer effects of some its constituents, most prominently lentinan (LNT), a polysaccharide substance in the beta-glucan family. Limited evidence from case reports and highly preliminary human studies hints that use of intravenously injected, purified lentinan might enhance the effectiveness of chemotherapy for stomach cancer, pancreatic cancer, and ovarian cancer.
123Note: Do not attempt to inject lentinan products designed for oral use.

Safety Issues

As a widely eaten food, shiitake mushroom is believed to be fairly safe. As with any food, allergic reactions can occur.
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The safety of concentrated shiitake extracts, however, is less clear. Safety in pregnant or nursing women, young children, or people with severe liver or kidney disease has not been evaluated.